President Biden and British Prime Minister Rishi Sunak on Thursday reaffirmed their continued intent to spearhead the Western alliance backing Ukraine, vowing after a White House meeting that the "special relationship" between their countries would endure despite recent chaos in the British political system.

The two leaders' comments came as Ukraine launched its long-anticipated counteroffensive against Russia, seeking to take back territory and relying heavily on U.S. efforts in recent months to prepare Kyiv's forces with advanced weapons and tactics.

Despite some recent calls by Republicans to limit U.S. expenditures on Ukraine, Biden said he was confident Washington would aid the besieged country as long as necessary. "I believe that that support will be real, even though you hear some voices today on Capitol Hill about whether or not we should continue to support Ukraine and for how long," Biden said.

Earlier this week, House Speaker Kevin McCarthy (R-Calif.) said the House has no plans to take up legislation that would boost military aid to Ukraine above levels included in the recent debt ceiling legislation, a position that put him at odds with Senate Minority Leader Mitch McConnell (R-Ky.) and Majority Leader Charles E. Schumer (D-N.Y.).

Biden warned that if Russia is not halted, its aggression is unlikely to end at Ukraine's borders. "I ask people to picture what would happen if we were not supporting [Ukraine]," he said. "Do we think Russia would stop in Kyiv? Do you think that's all there would be?"

Sunak, for his part, repeatedly thanked Biden for America's leadership in bolstering Ukraine, saying Washington had enabled "the forces of democracy and freedom to prevail."

He stressed that the United Kingdom had no plans to scale back its support. Addressing Russian President Vladimir Putin, Sunak said, "There is no point in trying to wait us out. We're not going anywhere. We will be here for as long as it takes."

Britain's 2016 vote to pull out of the European Union, a move known as Brexit, has raised questions about whether it would be as important an ally to the United States in the future. Biden's focus on protecting U.S. industry, meanwhile, has frustrated some American allies, who worry that they will be shut out of an important market.

Despite these uncertainties, the two leaders insisted Thursday that the friendship between their countries is ironclad.

Biden said that's because the United States and Britain share fundamental values. "That's the unshakable foundation of our special relationship - and it is a special relationship," the president said. "There's no country closer to the United States than the United Kingdom."

Sunak compared Biden's native city of Scranton, Pa., with his own hometown of Southampton, England.

"Ours is the indispensable alliance," Sunak said, adding, "You'll see the U.S. and the U.K. working even more closely together on all the biggest economic issues of our time, because that's what the moment demands."

The leaders said the two countries will work together in coming years on a series of urgent issues facing the globe, including artificial intelligence, climate change and quantum computing. Biden and Sunak will join the other NATO leaders for a summit in Vilnius, Lithuania, on July 11 and 12, a meeting that will bring them to Russia's doorstep.

Still, Biden, who often touts his long-standing personal relationships with world leaders, has not had that recently with Britain, whose Conservative Party leadership has been shaken by scandal and resignation. Biden has had little time to become close with Sunak - unlike, say, his friendship with Emmanuel Macron of France or Justin Trudeau of Canada.

Britain's flamboyant Boris Johnson resigned in September, ousted by his party as untrustworthy. Johnson's successor, Liz Truss, lasted just 45 days in office, after she struggled to right the British economy, making her the shortest-serving prime minister in British history.

Sunak, who made his first official trip to Washington this week, so far has provided some stability, and Thursday's meeting was the fourth consecutive month in which he and Biden have met in person. But Sunak and his Conservative Party face a national election next year, and recent polling has them trailing the left-leaning Labour Party.

In addition to their dialogue on Ukraine, Sunak and Biden discussed a range of economic issues including trade and emerging technologies. Sunak has said he wants Britain to be an innovator and watchdog on artificial intelligence, and aides say he proposed to Biden that the United Kingdom lead global efforts to regulate AI ahead of a summit he is hosting on the topic in the fall.

Without detailing specifics, Biden said that addressing the risks and potential of AI is a priority and that the two countries would "do more on joint research and development to ensure the future we're building remains fundamentally aligned with our values set in both of our countries."

Since Brexit, however, the United Kingdom's influence on some global issues has waned, and the United States and the European Union have made moves to cooperate on artificial intelligence without the British.

Still, Sunak's visit was in large part about making the case that, despite Britain's withdrawal from the E.U., enhanced economic cooperation between the United States and the United Kingdom is more critical than ever.

"I know some people have wondered what kind of partner Britain would be after we left the E.U.," Sunak said. "I'd say judge us by our actions. We're committed to our values as ever, as reliable an ally as ever, as attractive an investment destination as ever."

To that end, Biden and Sunak announced a new economic framework, the Atlantic Declaration, to enhance cooperation on a range of issues including critical and emerging technology, supply chains and clean energy. But the framework falls short of the type of comprehensive free-trade agreement that Sunak's Conservative Party campaigned on and Johnson promised after Brexit.

But it was enough for Sunak to return to London with some economic progress to tout.

"Be in no doubt, the economic relationship between our two countries has never been stronger," he said.

Biden and Sunak first met in San Diego in March, when they formally announced their plan to supply Australia with nuclear-powered submarines as part of an effort to counter China's growing influence in the Indo-Pacific. In April, they were both in Belfast as Biden commemorated the 25th anniversary of the Good Friday Agreement. They met again last month in Hiroshima, Japan, during a summit of the Group of Seven large democratic economies.

But all those were multilateral meetings, involving heads of state beyond Biden and Sunak. And so far, their relationship remains a far cry from the famed U.S.-U.K. political romances of the past, including those of Bill Clinton and Tony Blair or Ronald Reagan and Margaret Thatcher.

Some British observers felt snubbed during Biden's recent trip to Ireland, when he repeatedly highlighted his connection to the country and openly wondered why his ancestors ever left, but did not bother to stop in neighboring Britain. Then he skipped the coronation of King Charles III, sending the first lady in his place.

Sunak has yet to receive an invitation for a state dinner, after the leaders of both France and South Korea were feted with such events at the White House. Later this month, Indian Prime Minister Narendra Modi, too, will travel to Washington for a state dinner.

White House officials play down the notion of any distance between the two leaders or their nations, noting that no American president has attended a British coronation (Dwight D. Eisenhower sent a delegation to Queen Elizabeth II's coronation in June 1953). Biden has accepted an invitation from King Charles for a state visit, which could come as soon as next month.

Sunak, 43, is seen as a steady leader in Britain, if not a massively popular one. A former Goldman Sachs banker and a technology expert, he received his MBA at Stanford University. Alongside his wife, Akshata Murty, who owns vast shares of her father's India-based tech company, Infosys, the couple are among the richest in Britain.

When Biden and Sunak met in San Diego earlier this year, the president welcomed the British leader's American ties, while also taking the opportunity to poke fun at his immense wealth.

"I want to welcome him back to California," Biden said. "He's a Stanford man, and he still has a home here in California. That's why I'm being very nice to him - maybe he'll invite me to his home here in California."

Sunak arrived in Washington on Tuesday night and stayed at the Blair House. He paid a visit to Arlington National Cemetery on Wednesday, followed by meetings on Capitol Hill with House and Senate leaders. He concluded the night by attending the Washington Nationals baseball game, but much to the British press's chagrin, he did not throw out the first pitch.

And by Thursday, he departed Washington with firm assurances on the status of the special relationship.

When asked about the U.S.-U.K. relationship before sitting down with Sunak in the Oval Office, Biden gave a thumbs-up and said it was "in real good shape."

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Booth reported from London.

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